Arteriosclerotic plaque deposits which occlude and restrict the blood flow of coronary arteries are a major cause of heart disease. Treatment of such arteriosclerotic plaque has traditionally included open heart surgery or angioplasty.
Presently there is growing interest in the use of laser irradiation to remove arteriosclerotic plaque from occluded blood vessels, particularly coronary arteries. Such laser irradiation is delivered to the occluded vessel by means of a catheter comprising an optical fiber. Laser light is passed through the optical fiber and onto the arteriosclerotic plaque. A laser beam, thus delivered, has been found to remove arteriosclerotic plaque resulting in patency of the blood vessel.
For example, Circulation, Volume 66, Supplement II (October, 1982) at page 368 describes a method wherein a fiberscope including quartz fiber was inserted via the left subclavian artery to the aortailiac bifurcation in a dog. The right iliac artery was then successfully photoirradiated by YAG laser.
Circulation, Volumne 66, Supplement II (October, 1982) at page 366 describes a method using laser irradiation, delivered through a silicon fiber to the right iliac artery of rabbits to remove arteriosclerotic plaque.
The use of laser irradiation to remove arteriosclerotic plaque requires means to accurately position the end of the optical fiber with respect to the plaque which is to be removed. It also requires means to determine the thickness and hardness of the arteriosclerotic plaque deposit so that plaque removal may be maximized while arterial damage is minimized.
Methods for positioning the end of the optical fiber include X-ray fluoroscopy and/or viewing through a flexible fiberoptic scope inserted into the occluded artery. For example, U.S. Pat. No. 4,207,874 to Choy describes a device using X-ray fluoroscopy and viewing through a fiberoptic scope to locate obstructions in blood vessels and the like. Laser irradiation is then transmitted through an optical fiber to vaporize the obstruction.
X-ray fluoroscopy methods involve the positioning of the catheter tip by the injecton of a radiopaque material into the occluded blood vessel and viewing the X-ray shadow images of the artery and the catheter by a fluoroscope. Such images do not generally give sufficient detail of the occluded blood vessel to accurately and safely position the catheter tip with respect to an arteriosclerotic plaque deposit. Further, X-ray fluoroscopy methods also provide little information regarding thickness and density of the plaque deposits.
Fiberoptic scopes have both illumination and viewing capabilities but require blocking of the blood flow through the blood vessel followed by flushing of the blood vessel with a clear liquid such as saline, until a clear pathway is achieved. Viewing can then be done with the eye directly or, for example, with a television camera and monitoring system.
There are several disadvantages associated with the fiberoptic scope methods, including the fact that viewing cannot be done during laser irradiation and that the blood flow must be stopped during viewing. Further, viewing by a fiberoptic scope reveals little or no information with regard to the thickness or density of the arteriosclerotic plaque deposit. Also, fiberoptic scopes tend to be very expensive and generally have only a limited life before costly repairs are required.